Prostate and breast cancer are significant health problems in North America. Treatment of these diseases rely on the ability of antiandrogens (in the case of prostate disease) and antiestrogens (in the case of breast cancer) to induce apoptosis in tumor cells, which are largely of epithelial origin. While often initially successful, tumors which are refractory to hormone-based therapies often emerge. Studies of apoptosis in prostate and mammary tissue have demonstrated that one of the genes that is upregulated in dying cells is IGFBP-5 (a member of the insulin- like growth factor binding protein family). This protein appears to sequester IGF-I away from its receptor through interactions with specific components of the extracellular matrix which leads to the induction of apoptosis in the epithelial cells of the glands. IGF-I, therefore, appears to be an essential growth factor that is required for the survival of epithelial cells. Since disruption of the IGF-I signaling pathway leads to cell death, Dr. Tenniswood and coworkers propose to: A) fully characterize the changes in the IGF-I axis in vivo, in prostate and mammary gland prior to and following hormone ablation, using immunohistochemistry and in situ hybridization coupled with Western and Northern analysis; B) demonstrate that IGFBP-V is induced in vitro in hormone-dependent prostate and mammary tumor cell lines by antiandrogen and antiestrogen therapies using immunohisto- chemistry, Western and Northern analysis; C) establish the causative role of IGFBP-5 by transfection of an inducible IGFBP-5 construct under prostate and breast cancer cell lines and by exogenous addition of recombinant IGFBP-5 to the cell cultures; D) establish the role of specific components of the ECM and the sequestration of IGFBP-5 and the attenuation of IGF-1 signaling by growing cells on specific matrices and determining whether they retain sensitivity of IGF-5 overexpression; E) determine if tumor cells that are insensitive to standard hormonal therapies are sensitive to IGF-1 ablation and whether insensitive cells can be rendered sensitive by growing them on the appropriate components of ECM. Finally, to obtain a better understanding of the molecular biology of cell death in prostate and breast cancer cells mediated by IGF-1, he will use RT- PCR in differential display to identify genes that are induced after IGF-1 ablation in mammary and prostate tumor cell lines.